Research On Experiment Effect And Influence Factors Of Forward And Reverse Displacement In QZ Oilfield

In late years,huge amounts of newly proved crude oil reserves in China pertain to low permeability and ultra-low permeability reservoirs,which usually have the disadvantages of low natural productivity,rapid decline of formation pressure,insufficient formation energy and low recovery degree.The study area of this paper is QZ oilfield which has entered the high water cut stage.This area belongs to a typical ultra-low permeability reservoir with low waterflooding efficiency and declining development effect.A great amount of highly dispersed residual oil detains in the oil layer.At present,there is insufficient understanding of dynamic residual oil research and oil-water motion laws in this block.In order to further tap the potential and enhance the recovery ratio,this paper alters the drive orientation through the positive and negative displacement technology,forcing the displacement channel and displacement pressure conditions to change,so as to change the remaining oil occurrence state and activate the remaining oil at the micro and macro levels,and effectively employ the remaining oil in the middle and late stages of QZ oilfield development.Firstly,the physical model experiment of forward and reverse water flooding was carried out.It was found that after the forward water flooding reached the limit,the oil recovery increased by only 2.5 % even if the flow velocity of reverse displacement was continuously increased;then we carry out indoor water drive contrast experiments to determine the best reverse time.The water flooding direction was changed under different injection volumes.By comparing the final oil recovery,it is known that: when the displacement direction is changed at the initial stage of water drive development(injection rate is 0.51 pv,recovery rate is 32.61 %),the recovery is increased by 7.39 % compared with the positive recovery.At this time,the maximum oil recovery is achieved.Based on the two experiments,it can be known that the water flooding effect is the best when the direction is changed at the initial stage of water flooding development.Meanwhile,combined with CT scanning technology and microscopic displacement experiment,we can observe the oil-water occurrence state and analyze the mechanism of oil-water production in different displacement stages,so as to effectively develop the remaining oil in ultra-low permeability reservoirs.From the micro point of view,the reverse water drive model based on phase field method is established to study the influence of different water drive pressure and rock wettability on the reverse oil displacement efficiency and oil-water migration.Sum up oil-water flow law in micropore during displacement.The results show that too high or too low injection pressure will lead to poor oil displacement effect,and hydrophilic formation is more conducive to reverse water flooding.The research results of this paper provide a reference for building the framework of reverse water flooding and EOR,which is of great significance for the sustainable development of QZ oilfield.